1. Field of the Invention
The invention relates to a planar magnetic field probe. Particularly, the invention relates to a planar magnetic field probe capable of suppressing electric field coupling and having high sensitivity.
2. Description of Related Art
A near-field magnetic field probe is generally designed as a handheld device, which can be used to measure electromagnetic radiation of an electronic device, or used to position a possible electromagnetic radiation source of the electronic devices.
The magnetic field probe is generally made in the form of a loop. The probe is connected to a measuring instrument (an oscilloscope or a spectrum analyser, etc.) through a transmission line. The measuring instrument obtains a magnetic field strength according to a signal (for example, a voltage signal or a current signal) measured from the transmission line. Taking a digital circuit as an example, the digital circuit generally has a plurality of current loops which generate magnetic fields and the magnetic field probe can be used to measure and analyse the related magnetic fields.
A single loop magnetic field probe is mainly used in the related arts. There are two components of current on the PCB. One is the current on the ground plane and the other is the current on the trace. When the fast transient pulse is injected into the ground plane, the magnetic fields of the trace currents are often much weaker than the magnetic field of the surface current. Therefore it is difficult to measure trace currents by the same magnetic field probe that is used for the ground layer current. However, the field components are different. The trace current has a normal field component. It is possible to separate the trace current by measuring the normal field component over the PCB.
FIG. 1 is a schematic diagram of a conventional method of measuring a magnetic field. A magnetic field Hg generated by the current of a ground layer G1 has two components in X and Y directions, and a magnetic field HS generated by a current I1 of a signal line S1 has three components in X, Y and Z directions. When measuring the magnetic fields, a loop normal of conventional magnetic field probe 102 is perpendicular to the normal of a circuit board 104 and is placed close to the surface of the signal line S1. The magnetic field probe 102 simultaneously measures the magnetic field Hg generated by the current of the ground layer G1 and the magnetic field HS generated by the current I1 of the signal line S1 in the X and the Y directions. Since the current I1 of the signal line S1 is much weaker than the current of the ground layer G1, it is difficult to use the conventional magnetic field probe 102 in measuring the magnetic field Hg generated by the current I1 of the signal line S1.